Most meters are calibrated to measure the volume of liquid flowing through them in terms of gallons or cubic feet or the metric equivalent measures. Obviously since the temperature affects the density of the liquids, different volumes will be sensed by the meter at different temperatures for the same weight of liquid. For example, jet aircraft fuel has a high coefficient of expansion, resulting in a much higher weight of fuel for a given measured volume at 32.degree. F. than at 80.degree. F. In an environment where there are changing temperatures, it is not possible to accurately calculate the actual weight of the fuel measured in gallons unless a gallon/minute vs. temperature chart is available. Even then, only an approximation is available. Further, even if the chart is available, the continuous API gravity reading of the liquid or fuel must be known to better calculate the actual weight of liquid or fuel passing through the meter.
Currently, the fuel industry often sells by weight due to the wide range of American Petroleum Institute API densities of fuels at a given installation, as it is the most accurate method of determining the value sold and received. Fuel densities from API 32 to API 60 are quite common at some installations and require numerous meters and complex record keeping to approximate the weight of the fuel for a given number of gallons passing through a calibrated meter.
U.S. Pat. No. 3,283,575 issued to A. J. Granberg illustrates a temperature compensation device for a meter, and U.S. Pat. No. 3,020,758 issued to A. J. Granberg illustrates structure which adjusts a meter for changes in specific gravity. Also, U.S. Pat. No. 3,224,273 issued to A. J. Granberg discloses structure which adjusts a meter register or counter for changes in temperature or gravity. See U.S. Pat. No. 2,806,374 issued to A. J. Granberg regarding transmission systems for adjusting meter readings for calibration and compensations. These devices are related to the current invention, but cannot provide simultaneous dual readings of volume and weight.
Obviously, there is a need to have an accurate weight reading of liquid passing through positive displacement liquid meters, particularly when fuel is sold. Jet aircraft fuel consumption, for example, is measured in pounds per hour, and therefore most commercial jet operators would prefer to buy fuel by weight when possible, as it is more relevant to actual operation, as well as to value received.
The instant invention is designed to provide an accurate reading in gallons on one register, which is automatically and simultaneously converted into pounds or kilograms on a second or different register. By first converting the meter flow to accurate volume readings, such as gallons, and simultaneously converting this volume reading to pounds with appropriate compensation, very accurate weight can be directly read from the weight register at all times.